Heretofore, a power semiconductor module (a power module) for large current such as IGBT (Insulated Gate Bipolar Transistor), a power MOS-FET, and a power transistor is known as a switching device. Such power module is installed in a hybrid vehicle, an electric vehicle, and others. Since a semiconductor element generates a large amount of self heating during operation, the in-vehicle power module needs to include a cooling structure having a high heat dissipation performance.
FIG. 13 shows one example of the power module including a cooler. A power module 90 includes a plurality of semiconductor elements 10 which are heating elements, a heat sink 20 to which the semiconductor elements 10 are soldered, and a cooler 30 including flow channels 33 formed by cooling fins 31 and a cover plate 32. With this structure, the heat generated in each semiconductor element 10 is transferred to the entire heat sink 20. The transferred heat is exchanged by a coolant flowing in the cooler 30, thereby effectively cooling each semiconductor element 10.
The heat sink 20 and the cooler 30 need to be electrically insulated from each other. Thus, both are bonded to each other through insulating resin. It is further necessary to prevent deterioration of the heat transfer coefficient between the heat sink 20 and the cooler 30. Accordingly, the insulating resin used therein is high heat conductive resin that exhibits good heat conductivity.
Herein, in the case of using the high heat conductive insulating resin in the form of a sheet, this sheet is bonded to the cooler 30 in advance, and the heat sink 20 is pressed (pressurized) against the sheet while the sheet is being heated, thereby bonding the sheet to the heat sink 20.
Alternatively, in the case of using the high heat conductive insulating resin in the form of a liquid, it is conceivable to bond the high heat conductive insulating resin to the heat sink 20 by injecting and sealing the liquid resin into a predetermined region (between the heat sink 20 and the cooler 30) through an injection path, thus bonding the high heat conductive insulating resin to the heat sink 20.